The present invention relates in general to center pivot irrigation systems having a plurality of span units which are individually driven about the center pivot to irrigate a substantially circular area and more particularly to methods and apparatus for operating the system at a selectable average speed about the center pivot through hydraulic fluid drive means and methods and apparatus for controlling the distribution of the hydraulic fluid throughout the system in a manner to drive the units in a predetermined desired manner about the center pivot.
Various center pivot irrigation system have been developed heretofore wherein a plurality of water conduit sections are individually supported on self propelled carriages, individual conduit sections and carriages being interconnected with associated truss means to form an individual span unit with the individual units being interconnected in a substantially linear array extending from the center pivot out to an end span unit several hundred feet from the center pivot. Some of these prior center pivot irrigation systems have been driven through the use of hydraulic fluid systems operating hydraulically driven motor means associated with the individual span unit carriage wheels.
It has been the practice heretofore in prior hydraulically driven center pivot irrigation systems to maintain a relatively high system pressure supplied to each of the hydraulically driven motor means, such pressures being maintained generally through the use of a pressure compensation pump. The speed of the system about its center pivot has heretofore been controlled through the use of a flow control at the end span unit to attempt to run it at a given speed with the intermediate span units between the center pivot and end span unit having their fluid flow controlled in order to follow or keep up with the end span unit. These prior systems have not proven to be entirely satisfactory in that the high system pressures required require an expensive hydraulic fluid system and the means of speed control through attempted control of the end span unit with attendant follow-up control of the intermediate span units has not produced a fully satisfactory speed control for the system. In addition, when reversing the direction of travel of the system about the center pivot, it has been found that the lag of the intermediate units relative to the end span unit cannot be maintained as small as would be desirable and as might be attainable if the system were originally designed to go in one direction only about the center pivot.
It is therefore been recognized that there is a need for an improved method and apparatus for driving a center pivot irrigation system through hydraulic means to provide a better speed control about the center pivot and to reduce the lag of intermediate span units relative to the end unit while the system is traveling in either of two reversible directions about the center pivot.